In various semiconductor devices, it is often desirable, advantageous, and/or necessary to form one or more trenches in the substrate on which the device is being formed and/or in the various materials deposited on the substrate during the manufacture of the device. Such trenches may serve various purposes including, but not limited to, isolation of one region from another, or for example, in superjunction semiconductor devices such trenches can provide access to the drift region for doping.
Superjunction devices are an increasingly important type of semiconductor device that are designed for high voltage applications where decreased on-resistance is highly advantageous. Since the invention of superjunction devices by Dr. Xingbi Chen, as disclosed in U.S. Pat. No. 5,216,275, the contents of which are herein incorporated by reference, there have been many attempts to expand and improve on the superjunction effect of his invention. U.S. Pat. Nos. 6,410,958, 6,300,171 and 6,307,246 are examples of such efforts and are incorporated herein by reference.
In many semiconductor manufacturing processes, when a trench is desired, the trench recess is etched into the substrate. The trench is optionally surface treated to remove residues and/or roughened surfaces, and subsequently filled with a dense, high-quality insulating dielectric material. This process presents various problems in subsequent manufacturing and/or use. First, the dielectric material will often have thermal properties that are different from the surrounding substrate, which creates various forms of stress under normal operating temperatures and during subsequent high temperature fabrication steps. As one material expands differently than the other, defects can appear in the device. Second, in certain devices where trenches are relatively deep compared to their width, filling the trench can be difficult and can add cost and complication to the manufacturing process. Third, uncontrollable mobile ions often become incorporated in a filling material, resulting in potentially unstable high-voltage breakdown characteristics.
Prior attempts at solutions to the aforementioned problems have included the use of so-called empty trenches, wherein a trench is formed between two regions to be separated and subsequently lined with an oxide and simultaneously sealed at the upper opening of the trench, thereby forming an air filled buffer between the two regions. While such methods may alleviate the difficulties associated with completely filling deep trenches with a dielectric material, the lining of the trench in conjunction with the formation of the upper seal does not adequately alleviate the problems associated with divergent thermal properties between a substrate and trench lining materials.
Thus, there is a need in the art for semiconductor device structures with trenches suitable in various device designs that do not require filling and do not suffer from the aforementioned thermal complications.